Back-End of the Line Compatible Growth of Wafer Scale MoS₂ Bilayer for Neuromorphic Device Application

The back end-of-line (BEOL) compatible and scalable growth of two-dimensional (2D) transition metal dichalcogenides for device applications has been the most challenging task for their industrial adoption. In this study, 2D MoS₂ bilayer has been synthesized across 4-inch SiO₂/Si substrate using plasma enhanced chemical vapor deposition (PECVD) technique at temperature below 350 °C. Raman and photoluminescence (PL) spectra show the formation of pure and high-quality bilayer MoS₂. The growth is optimized by varying the PECVD parameters such as plasma power, Ar/H₂S gas ratio, seed layer thickness, growth time and substrate temperature. The AFM and HRTEM reveal the morphological and structural characteristics of the film. XPS measurements gives the chemical state and composition of the as-grown film. Filed effect transistor (FET) characteristics of the as fabricated device on the MOS₂ film show an Ion/Ioff ~10³ and a mobility of 0.2 cm²V^-1s^-1. Further, the FET device exhibits essential synaptic behaviour such as short-term plasticity, long term and short-term potentiation and depression with high linearity and stability.